Compressors and vacuum pumps which use a liquid to effect compression of the gas are known. One widely used type of compressor is the liquid piston liquid ring type which has a rotor or impeller which turns freely inside a cylindrical casing on a center eccentric to that of the casing. The rotor is smaller than the casing and has a number of curved vanes which form open-ended buckets. As the rotor revolves, it carries round with it a working fluid, usually water, which forms a ring around the casing. Because of the eccentric positioning of the rotor axis, the liquid enters and leaves the buckets as the rotor revolves and this movement of the liquid is used to compress the gas. Suitable inlet and discharge ports are provided at the center of the rotor.
A variant of the liquid piston pump has an oval casing which permits two compression cycles for each revolution of the rotor.
Eductors are often used for vacuum systems in preference to compressors with moving parts because they are simple, cheap, easy to operate and require little maintenance. They may also be used to compress a gas or vapor, for pumping a liquid or for contacting two fluids.
The principal disadvantages of the liquid piston compressor are that it has a low efficiency and limited compression ratio. Eductors also have a very low efficiency and a limited compression ratio.
A rotary ejector compressor was proposed by Eskeli in U.S. Pat. No. 3,719,434. This device employs a rotor to accelerate a working fluid to entrain the gas which is then compressed in a vaned casing around the rotor. The compressor may also be used as a vacuum pump, in common with many other compressors.